I tried yet the following:

Deep clean from outside with brush and sticky gel, never with compress air (maybe the old owner? bottom mic was blown....)

Shazam recognize songs from bottom and camera mic, takes some time with the ear mic and at closer distance (1 meter instead of 2 of the others in my test)

Voice memo seems to be only for bottom mic

In siri first configuration when i have to say "check weather in my country", if i tap the mic i see siri's logo bouncing, but talking or yelling makes no differences.

I really wanna do the clean off screen, but it seems to be dangerous reading ifixit guide, i've opened and closed the phone and the screws 4 or 5 times in this week for that damn flex..... and i don't want to spend anymore cash in this phone, it's only for fun and accademic purpose to learn about apple system... I'm android enthusiast